Continuous monitoring of vital signs with the ability to remotely monitor patient status is a growing field and the ability to incorporate multiple measurement capabilities into a single small unobtrusive patch that can be worn by a patient (i.e., a body worn patch) for multiple days at a time is a desirable feature. One such measurement is blood oxygen reading, often carried out by a pulse oximeter. Current pulse oximeter designs use a high precision current sink to control light emitting diodes (LED's) which are driven with a voltage controlled source. A patient's blood oxygen reading may be influenced by the patient's level of activity, and therefore measurements that may be taken by a patch may be misleading if the readings are provided with no context regarding the patient's activities.